1. Field of the Invention
The present general inventive concept relates to a portable recorder, and more particularly, to a noise removing apparatus and method capable of efficiently removing noise when a voice signal with noise is input to the portable recorder.
2. Description of the Related Art
Generally, a portable recorder records a voice signal through a microphone. However, in a conventional portable recorder, a voice signal is recorded together with external environmental noise or contact noise and, as a result, sound quality is degraded when the voice signal is reproduced.
Accordingly, a noise removing technology to remove this environmental noise is needed. In general, a spectrum noise removing apparatus employs a spectral subtraction method in order to remove background noise.
The spectral subtraction method will now be explained with reference to FIG. 1.
First, an analog signal of one channel input to a microphone is converted into a digital signal. Then, framing of the digital signal is performed on a time axis domain. The frame unit signals are windowed in order to reduce information discontinuation between the frames and to reduce distortion. A fast Fourier transform (FFT) unit 110 converts the windowed signals to a frequency spectrum having spectrum information through Fourier transform.
This spectrum information is composed of magnitude spectrum information and phase spectrum information. Here, the magnitude spectrum information is used for spectral subtraction and the phase spectrum information is used for inverse fast Fourier transform (IFFT).
A noise detection unit 120 determines whether the signal of a current frame FFT-processed in the FFT unit 110 is a frame including only noise or a frame including a voice signal with noise.
If it is determined by the noise detection unit 120 that the current frame is a noise frame, a noise spectrum unit 130 stores a spectrum shape of the noise frame.
A spectral subtraction unit 140 performs subtraction of an estimated noise spectrum from the magnitude spectrum in which voice and noise are mixed.
A noise spectrum that is estimated when a noise characteristic is normal is similar to the spectrum of an actual noise component. Accordingly, the magnitude spectrum obtained by the spectral subtraction is approximately the magnitude of the voice signal from which the noise is removed.
An IFFT unit 150 performs IFFT transform of an audio spectrum output from the spectral subtraction unit 140 and restores an original signal to the time domain.
The FFT unit 110, which converts the time domain signal into the frequency domain signal and the IFFT unit 150, which restores the frequency domain signal to the time domain, require the largest amounts of computation. Accordingly, since the FFT and IFFT operations require considerable parts to perform computation in the conventional noise removing system, it is difficult to apply the system to a portable recorder.